| 1. |
- Moros, M, et al.
(author)
-
Were glacial iceberg surges in the North Atlantic triggered by climatic warming?
- 2002
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In: Marine Geology. - 0025-3227. ; 192:4, s. 393-417
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Journal article (peer-reviewed)abstract
- High-resolution physical, mineralogical, sedimentological and micropalaeontological studies were carried out on North Atlantic cores from the Reykjanes Ridge at 59degreesN and from the region southwest of the Faeroe Islands. All core sites are situated along the pathway of Iceland-Scotland Overflow Water (ISOW) and the various parameters measured display similar features. Previously identified carbonate oscillations [Keigwin and Jones (1994) J. Geophys. Res., 99, 12397-12410] in the time span back to the Marine Isotope Stage 5-4 transition and Late Glacial lithic events [Bond and Lotti (1995) Science, 267, 1005-1010], such as the Heinrich ice-rafting events, are all represented in the core records. Long-term trends and higher-frequency changes in ISOW intensity were reconstructed on the basis of various independent proxy records. The long-term trends in circulation match theoretical orbitally forced insolation changes. Our observed links between ice-rafted detritus (IRD) input, variations in sea surface temperature (SST) and circulation at greater depth point to the need to re-examine the origin of IRD events. We suggest that these events may have been triggered by enhanced, partly sub-surface, heat transport to the-north. Enhanced northward heat transport may have caused bottom melting of floating outlet glaciers and ice shelves, leading to increased iceberg discharge and ice sheet destabilization. This discharge. resulted in lower SST's and a lower temperature over Greenland. Thus, as shown by our records, this scenario implies a temporary de-coupling of surface processes and circulation at greater depth. A key feature is the occurrence of a-saw-tooth pattern in the marine data, which is similar to the Greenland ice core records. Moreover, the 'warming' theory of IRD events would explain the observed 'out-of-phase' relationship between the Greenland and Antarctic ice-core records and also the rapid establishment of higher temperatures over Greenland immediately after the cold phases (stadials) of the Dansgaard-Oeschger cycles.
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| 2. |
- Rasmussen, Tine, et al.
(author)
-
The Faroe-Shetland Gateway: Late Quaternary water mass exchange between the Nordic seas and the northeastern Atlantic
- 2002
-
In: Marine Geology. - 0025-3227. ; 188:1-2, s. 165-192
-
Journal article (peer-reviewed)abstract
- Thirteen piston and gravity cores from the Faroe-Shetland area were investigated for their planktic and benthic foraminiferal and oxygen isotopic distributions. Eight time-slices between 18 ka BP and the present were reconstructed to study variations in surface and deep water exchange between the SE Norwegian Sea and the northeast Atlantic Ocean. Today, a relatively strong northward flow of warm North Atlantic surface water is counterbalanced by a southward outflow of newly convected cold bottom water, the Norwegian Sea Overflow Water. During the last glacial maximum at 18 ka BP both the surface and bottom flows were slow and the climate conditions were Arctic. The convection north of the Faroe area was weak and unstable. The first indication of the deglaciation is a decrease in the planktic oxygen isotope values discernible southwest of the Faroe Islands at 15.5 ka BP. The deglaciation proceeded northeast and eastward synchronous with a gradual intensification of northward flowing warmer Atlantic Intermediate Water along the sea bottom. Meltwater fluxes increased between 14 and 13 ka BP producing cold surface waters, and the climatic cooling was extreme. There was no southward overflow of cold bottom water during this time period and the exchange of water masses between the Nordic seas and the North Atlantic Ocean was essentially reversed, i.e. estuarine. During the Bolling Interstadial at 12.5 ka BP northward flowing warm surface water was present to the east of the Faroe-Shetland Channel, wedged below a tongue of polar water spreading from the northwest and reaching into the Faroe-Shetland Channel. Convection in the Nordic seas and overflow of cold deep water started during the Bolling Interstadial. The polar water spread more eastward and southward during the following cold spell, the Younger Dryas, around 10.3 ka BP. The polar water was overlying the warmer, but more saline Atlantic water, which flowed northward below the cold surface water. The overflow of cold bottom water was supposedly only slightly weaker than during the Bolling Interstadial. Strong inflow of warm surface water took place during the Early Holocene at 9.5 ka BP and relatively dense cold water flowed southward along the bottom. The rate of water mass exchange reached a maximum at 6.5 ka BP, when both the inflow of warm Atlantic surface water and the outflow of cold dense bottom water appear to have been stronger than today.
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| 3. |
- Schwarzer, K, et al.
(author)
-
Coastline evolution at different time scales - examples from the Pomeranian Bight, southern Baltic Sea
- 2003
-
In: Marine Geology. - 0025-3227. ; 194:1-2, s. 79-101
-
Journal article (peer-reviewed)abstract
- Sedimentological and morphological changes on the upper and lower shoreface during relatively stable sea-level highstand conditions have been investigated in the Pomeranian Bight, southern Baltic Sea, at time scales ranging from storm events to millennia. In order to cover that variety of time scales, different methods have been applied. Seasonal variations in the morphology of the upper shoreface were measured accurately using the tracer stick method. The ratio of breaking waves and energy dissipation due to wave breaking are the main forces controlling redeposition on the upper shoreface with the depth of disturbance up to three times the net change. The impact of single storm events can be observed from sidescan sonar mosaics to remain on the decadal scale. Aerial photographs covering the upper shoreface show that the location of gates, channel-like systems where water masses move offshore created during storm events, also remain stable over decades. Sedimentological and geomorphological variations and changes on the lower shoreface are only measurable on the century to millennium scale because the main driving forces are longlasting processes like sea-level fluctuations or neotectonics. Data on these scales have much more uncertainty in their relationship to forcing functions than data at shorter time scales. Because the effects of coastal processes active on different time scales can interact, comprehensive understanding of large-scale coastal behavior requires investigations from short events to long-term processes. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 4. |
- Ask, Maria
(author)
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Mechanical tests on claystone from Ocean Drilling Program Hole 1070A (Leg 173) : implications for elevatedpore-fluid pressure in sediments within the ocean-continent transition zone, West Iberia
- 2001
-
In: Marine Geology. - 0025-3227 .- 1872-6151. ; 177:3, s. 395-410
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Journal article (peer-reviewed)abstract
- Laboratory geotechnical deformation tests on a claystone test specimen from 619 m depth in Ocean Drilling Program Hole 1070A provide evidence of low effective yield stresses and capillary pressures (1.2–1.5 MPa) in the sediment section near the acoustic basement. Effects from negative pore-fluid pressure, and the presence of expansive clay minerals probably account for the drastic change in the mechanical behavior of the sample below and above the yield stress. The results from the geotechnical tests, together with high porosity values, suggest that the pore-fluid pressure is high in these basal sediments. The intense fracture/vein development in the basement suggests that the pore-fluids originate from deeper sections in the basement. Porosity anomalies are found near the basement in three boreholes drilled in the western part of the Iberia Margin. The anomalies are interpreted to signal elevated pore-fluid pressure. Consequently, a zone of overpressure possibly exists in the western part of the ocean-transition zone of the West Iberia margin, which thickens towards the west.
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| 5. |
- Boström, Kurt, et al.
(author)
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Geochemistry and origin of ferromanganese concretions in the Gulf of Bothnia
- 1982
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In: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 50:1-2, s. 1-24
-
Journal article (peer-reviewed)abstract
- Ferromanganese concretions cover large areas of the Gulf of Bothnia. They are flat to well-rounded, the rounded ones being richer in oxyhydroxides of iron and manganese. Rounded and ellipsoidal nodules, particularly those in the northern Gulf of Bothnia, are richest in Mn, Ni, Ba and Cu, which probably coexist in a Mn oxyhydroxide phase. Flat nodules are enriched in Fe, P, rare earths and As, probably associated with an Fe oxy-hydroxide component. Aluminum, V, Cr and Ti occur in still another phase. The sediments of the gulf generally consist of a 10-50 mm-thick layer of oxidized surface sediment, enriched in Mn, Ba, P and Ni lying on top of reduced sediments which are diagenetically depleted in these elements. The remobilized elements have redeposited in the nodules, but this process cannot explain the origin of all the nodular material. Some released Mn, Ba and Ni furthermore enter into suspended phases, which eventually leave the Baltic Sea. The economic value of the nodules in the Gulf of Bothnia is probably limited at present.
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| 6. |
- Glaccum, R., et al.
(author)
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(Na, K)-phillipsite: Its stability conditions and geochemical role in the deep sea
- 1976
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In: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 21:1, s. 47-58
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Journal article (peer-reviewed)abstract
- Phillipsite occurs in the deep sea in areas of very slow sedimentation and as the final alteration product of basalt, suggesting that it is thermodynamically stable. The thermodynamic data for gibbsite, kaolinite, K-feldspar, Na-feldspar, analcime and H4 SiO4 (aq), as well as the activities of seawater constituents are reasonably well known. These values and estimated entropies for Na- and K-phillipsites permit an estimate of the free energy of formation (at 25°C) for Na-phillipsite (5337.6 ± 6.7 kcal/mole) and for K-phillipsite (5382.4 ± 1.9 kcal/mole). The decomposition of phillipsite to analcime at 250°C yields the same result, suggesting that phillipsite is indeed a stable mineral. Phillipsite does not regulate the concentration of Na+ and K+ in seawater, but probably affects the pH of bottom waters and the composition of interstitial waters. No indications exist of "frozen in" equilibria from hydrothermal reactions at 100-200°C as could be expected by submarine volcanism.
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| 7. |
- Ingri, Johan
(author)
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Geochemistry of ferromanganese concretions in the Barents Sea
- 1985
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In: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 67:1-2, s. 101-119
-
Journal article (peer-reviewed)abstract
- Ferromanganese concretions from ten stations in the Barents Sea have been analysed for 24 elements. The deposits occur as discoidal and flat concretions and as coatings, in the latter case on lithified or detrital material or as extensive pavements on the Svalbard shelf. The concretions are compositionally similar to Baltic concretions but differ considerably from deep-ocean nodules, particularly in Cu, Ni and Co contents. Statistical analyses reveal distinct correlations between Mn, Na, Ba, Ni and Cu; the Mn-rich coatings showed enrichment of Mo, Zn and possibly Co in a Mn-phase. The iron phase holds high concretions of P and As. Two iron-rich concretions with high contents of P, Ca, Sr, Y, Yb and La were found east and northeast of Spitsbergen Banken, probably indicating upwelling of nutrient-rich, cold polar water along the Svalbard shelf.
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| 8. |
- Sohlenius, Gustav, et al.
(author)
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Development of anoxia during the Holocene fresh-brackish water transition in the Baltic Sea
- 2001
-
In: Marine Geology. - : Elsevier. - 0025-3227 .- 1872-6151. ; 177, s. 221-242
-
Journal article (peer-reviewed)abstract
- One of the most pronounced environmental changes during the Holocene Baltic Sea history was the transition from the freshwater Ancylus Lake to the brackish water Litorina Sea. The establishment of brackish conditions during this transition (the A/L) was caused by an interplay of sea level rise and subsidence of sills in the Danish Straits. The northward progression of salt water influence caused the gradual and transgressive development of a halocline which obstructed vertical water circulation in the deep depositional basins. It caused changes in surface water properties (mirrored by diatom flora and productivity levels), in redox conditions of bottom waters, in organic carbon preservation of sediments, and in nutrient cycling. In seven cores from the Arkona, Bornholm and Gotland Basins, the A/L transition was WC dated and studied in high-resolution samples for minor and major element composition. The earliest marine inflows were small and can only be detected by sedimentary properties in the southern Baltic. Further north the salinity increase was gradual and retarded; only when the connection through the Danish Straits was well established the entire Baltic proper became brackish with a stratified water column. This development took altogether 2000 C-14 yr (c. 9000-7000 BP). Diatom analyses indicate a fast increase in salinity c. 7000 C-14 yr BP, which coincides with a transgressive phase in the straits, In the Gotland Basin, deposition of laminated sediments and periodically euxinic conditions were established first at the deepest bottoms, and rose to shallower water depth as the basin was gradually filled with dense brackish water. The laminated sequences have high organic carbon contents, which is attributed to better preservation under anoxic conditions. Litorina sediments from the Arkona and Bornholm Basins are bioturbated even though conditions became more reducing also in these sediments during the A/L transition. The development of reducing conditions during the A/L transition probably caused Pre-mobilization from the sediments and a decrease in the rates of denitrification. Both factors increased primary productivity. A comparison between isochronous sediments from different basins shows that certain elements (Mo, Cu, V and Cd) are enriched sediments deposited during predominantly anoxic conditions.
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| 9. |
- Sohlenius, Gustav, et al.
(author)
-
Holocene history of the Baltic Sea as recorded in a sediment core from the Gotland Deep
- 1996
-
In: Marine Geology. - : Elsevier. - 0025-3227 .- 1872-6151. ; 134, s. 183-201
-
Journal article (peer-reviewed)abstract
- A 4 m long sediment core from the Gotland Deep, Baltic Sea, was investigated by means of biostratigraphical and chemical parameters and C-14 datings. This multidisciplinary approach allows us to evaluate the regional changes in salinity and redox conditions during the Holocene. According to the diatom assemblages and C-14 datings, the sediments were deposited in the brackish and freshwater phases of the Yoldia Sea (10,300-9600 C-14 yr B.P.), the freshwater Ancylus Lake (9600-8000 C-14 yr B.P.) and in the brackish water Litorina Sea (8000-3000 C-14 yr B.P.). Of several palaeosalinity indicators evaluated, the diatoms are the least ambiguous. Nevertheless the B content and, under some premises, the C/S ratio may be used for palaeosalinity information. Iron sulphides in the lowermost freshwater sediments formed below the prevailing, oxic sediment-water interface. Pyrite in the uppermost freshwater sediments was to a large extent formed in Litorina time, by diffusion of Sigma H2S from overlying brackish water sediments. The Ancylus Lake/Litorina Sea transition can be traced by the marked changes in both the siliceous microfossil assemblages and in the chemical properties of the sediments. An early Litorina phase is characterised by increased primary production, progressively increasing salinity and the development of euxinic conditions. In the Litorina Sea laminated clay gyttjas (def. as a clay containing 6-30% organic matter) containing pyrite and laminae of Ca-rhodochrosite, (Mn,Ca)CO3, accumulated. Both these minerals formed in close connection with sediment deposition. The rhodochrosite laminae formed during occasional inflow of oxygen rich, marine water through the Danish Straits. Rhodochrosite is by far the most common mineral in the laminae and formed on average with a periodicity of two to three years.
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| 10. |
- Aldahan, AA, et al.
(author)
-
Be-10 records from sediments of the Arctic Ocean covering the past 350 ka
- 1997
-
In: MARINE GEOLOGY. - : ELSEVIER SCIENCE BV. - 0025-3227. ; 144:1-3, s. 147-162
-
Journal article (peer-reviewed)abstract
- Records of Be-10, Be-9, mineralogy and grain size were obtained from two cores collected by the Polarstern Expedition 1991 in the southern Nansen Basin (Core 2213-6) and the Yermak Plateau (Core 2208-2). The accumulation of sediments examined started from
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| 11. |
- Andresen, Camilla Snowman, et al.
(author)
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Holocene climate variability at multidecadal time scales detected by sedimentological indicators in a shelf core NW off Iceland
- 2005
-
In: Marine Geology. - : Elsevier BV. - 0025-3227. ; 214:4, s. 323-338
-
Journal article (peer-reviewed)abstract
- A Holocene sediment record is presented from the Djupall trough, situated on the inner shelf northwest of Iceland. The paleoclimatic development has been interpreted on the basis of mass accumulation rate, carbonate content, mean grain size, sediment petrology and 29 radiocarbon dates. The results demonstrate in the early Holocene (10,000-8000 cal year BP) high sediment accumulation rates attributable to the effect of enhanced sediment mobilisation under influence of a relatively low sea level and remobilisation of glacial sediments on the sparsely vegetated Vestfirdir peninsula. The data suggest that a general southward displacement of the Polar Front commenced around 5000-4000 cal year BP. A new proxy for Holocene climatic variability is presented by the basalt/plagioclase ratio in the 63-100 mum fraction. High basalt/plagioclase values are primarily related to periods of increased storminess and bottom current energy, which enhanced the transport of basaltic sediment from the coastal zone towards the outer shelf. Advection of polar waters containing basalt-rich IRD from the eastern Greenland Blosseville Kyst basalt province may also have contributed to increased basalt/plagioclase ratios. The correlation between basalt/plagioclase ratios and proxies of solar activity (C-14 production and Be-10 flux) was explored and suggests that some of the centennial-scale peaks in colder climate could be related to increased nuclide production in the upper atmosphere. In addition, it was found that the Medieval Warm Period (c. 1100-700 cal year BP) was characterised by strong cyclone activity over the Iceland region. Intense atmospheric circulation during this period has been confirmed also by other studies in the northern North Atlantic region.
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| 12. |
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| 13. |
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| 14. |
- Erikson, Li, et al.
(author)
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Laboratory Investigation of Beach Scarp and Dune Recession Due to Notching and Subsequent Failure
- 2007
-
In: Marine Geology. - : Elsevier BV. - 0025-3227. ; 245:1-4, s. 1-19
-
Journal article (peer-reviewed)abstract
- Analytical models to calculate notch development and subsequent mass failure of dunes are presented. The notch evolution model is based on a transport equation for sediment from the dune and the sediment volume conservation equation, whereas the models of mass failure are derived using elementary engineering statics and soil mechanics. An empirical transport coefficient in the model describing the notch growth rate is found to be related to the hydrodynamic forcing at the dune normalized by geotechnical parameters describing the resistive strength of the dune. Two modes of mass failure are modeled whereby the overhang generated by the removal of material from the dune foot (notching) slides downward or topples over following the development of a tensile crack some distance shoreward of the maximum notch depth. The accuracy of the notch evolution and mass failure models are assessed by comparing calculated recession distances against measurements from a small-scale laboratory experiment.
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| 15. |
- Hernandez-Molina, F. J., et al.
(author)
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Oceanographic processes and morphosedimentary products along the Iberian margins: A new multidisciplinary approach
- 2016
-
In: Marine Geology. - : Elsevier BV. - 0025-3227. ; 378, s. 127-156
-
Journal article (peer-reviewed)abstract
- Our understanding of bottom-currents and associated oceanographic processes (e.g., overflows, barotropic tidal currents) including intermittent processes (e.g., vertical eddies, deep sea storms, horizontal vortices, internal waves and tsunamis) is rapidly evolving. Many deep-water processes remain poorly understood due to limited direct observations, but can generate significant depositional and erosional features on both short and long term time scales. This paper represents a review work, which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the Iberian continental margins. This review explores the implications of the studied processes, given their secondary role relative to other factors such as mass-transport and turbiditic processes, and highlights three major results: a) contourite depositional and erosional features are ubiquitous along the margins, indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation; b) the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient, including the contourite terraces development; and c) contourites deposits exhibit greater variation than the established fades model suggests. Therefore, a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development. An integrated interpretation of these oceanographic processes requires an understanding of contourites, seafloor features, their spatial and temporal evolution, and the near-bottom flows that form them. This approach will synthesize oceanographic data, seafloor morphology, sediments and seismic images to improve our knowledge of permanent and intermittent processes around Iberia, and evaluate their conceptual and regional role in the margin's sedimentary evolution. Given their complexes, three-dimensional and temporally-variable nature, integration of these processes into sedimentary, oceanographic and climatological frameworks will require a multidisciplinary approach that includes Geology, Physical oceanography, Paleoceanography and Benthic Biology.
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| 16. |
- Jennings, Anne E., et al.
(author)
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Baffin Bay paleoenvironments in the LGM and HS1 : Resolving the ice-shelf question
- 2018
-
In: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 402, s. 5-16
-
Journal article (peer-reviewed)abstract
- Core HU2008029-12PC from the Disko trough mouth fan on the central West Greenland continental slope is used to test whether an ice shelf covered Baffin Bay during the Last Glacial Maximum (LGM) and at the onset of the deglaciation. We use benthic and planktic foraminiferal assemblages, stable isotope analysis of planktic forams, algal biomarkers, ice-rafted detritus (IRD), lithofacies characteristics defined from CT scans, and quantitative mineralogy to reconstruct paleoceanographic conditions, sediment processes and sediment provenance. The chronology is based on radiocarbon dates on planktic foraminifers using a Delta R of 140 +/- 30 C-14 years, supplemented by the varying reservoir estimates of Stern and Lisiecki (2013) that provide an envelope of potential ages. HU2008029-12PC is bioturbated throughout. Sediments between the core base at 11.3 m and 4.6 m (LGM through HS1) comprise thin turbidites, plumites and hemipelagic sediments with Greenlandic provenance consistent with processes active at the Greenland Ice Sheet margin grounded at or near the shelf edge. Abundance spikes of planktic forams coincide with elevated abundance of benthic forams in assemblages indicative of chilled Atlantic Water, meltwater and intermittent marine productivity. IRD and IP25 are rare in this interval, but brassicasterol, an indicator of marine productivity reaches and sustains low levels during the LGM. These biological characteristics are consistent with a sea-ice covered ocean experiencing periods of more open water such as leads or polynyas in the sea ice cover, with chilled Atlantic Water at depth, rather than full iceshelf cover. They do not support the existence of a full Baffin Bay ice shelf cover extending from grounded ice on the Davis Strait. Initial ice retreat from the West Greenland margin is manifested by a pronounced lithofacies shift to bioturbated, diatomaceous mud with rare IRD of Greenlandic origin at 467 cm (16.2 cal ka BP; Delta R = 140 yrs) within HS1. A spike in foraminiferal abundance and ocean warmth indicator benthic forams precedes the initial ice retreat from the shelf edge. At the end of HS1, IP 25 , brassicasterol and benthic forams indicative of sea-ice edge productivity increase, indicating warming interstadial conditions. Within the Bolling/Allerod interstadial a strong rise in IP 25 content and IRD spikes rich in detrital carbonate from northern Baffin Bay indicate that northern Baffin Bay ice streams were retreating and provides evidence for increased open water, advection of Atlantic Water in the West Greenland Current, and formation of an IRD belt along the W. Greenland margin.
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| 17. |
- Kairytè, Milda, et al.
(author)
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Provenance of silt and clay within sandy deposits of the Lithuanian coastal zone (Baltic Sea)
- 2005
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In: Marine Geology. - : Elsevier BV. - 0025-3227. ; 218:1-4, s. 97-112
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Journal article (peer-reviewed)abstract
- Mineralogical analysis of the silt and clay fraction of sandy deposits of 37 surface samples and grain-size data are used to interpret sediment sources acting in the SE Baltic Sea along the Lithuanian coast. Mineralogical composition was determined using X-ray diffraction (XRD) methods. Grain-size distribution was obtained by standard dry sieving and pipette techniques. For identification of sources we combined known compositional information of possible sources with logical models for mineral combinations related to regional geological provinces and processes, supported by results of correlation and factor (principal component) analyses between minerals, grain-size parameters and bathymetric features of the area. The main sources supplying sediment into the area are: 1) the Sambian Peninsula to the south, 2) the Nemunas River, whose discharge passes through the Curonian Lagoon, and 3) Late Pleistocene till erosion on the sea floor in the north and at the Olando Kepure shore cliffs. The general pattern of spatial distribution related to the identified sources for the fine-grained sediment fraction is interpreted as a shore-parallel transport of suspended matter, flowing northwards in the southeastern part of the Baltic Sea. (c) 2005 Elsevier B.V. All rights reserved.
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| 18. |
- Kairytè, Milda, et al.
(author)
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Quantitative provenance of silt and clay within sandy deposits of the Lithuanian coastal zone (Baltic Sea)
- 2009
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In: Marine Geology. - : Elsevier BV. - 0025-3227. ; 257:1-4, s. 87-93
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Journal article (peer-reviewed)abstract
- A quantitative provenance approach is developed and in this study applied for the silt and clay fractions of sandy deposits along the Sea coast. Mineralogical composition of 37 surface samples was determined by X-ray diffraction (XRD). Grain-size distributions were obtained by standard dry sieving and pipette techniques. The characterization of mineralogical provenance is based upon known compositional information of possible sources, logical models for mineral combinations related to regional geological provinces and processes, and geographical features of the documented mineral distribution in the area of investigation. These interpretations are further supported by results of correlation and principal component analyses of mineral varieties, grain-size parameters and bathymetric features of the area. Partitioning of source contributions specific for each site of deposition is derived by solving simultaneous equations. Then, the quantified mineral composition at the initial source is reconstructed in the SE Baltic Sea along the Lithuanian coast, which serves as a test bed for the new method to quantify sediment sources The main sources supplying sediment to the area are: 1) Sambian Peninsula to the south (erosion of Pleistocene till and “Blue Earth” Paleogene sediments), supplying 33% of fine-grained sediment on average, 2) Nemunas River, the discharge of which passes through Curonian Lagoon and supplies an average 17% of the coastal fine sediments, and 3) Pleistocene till, eroded on the sea floor in the north and at the Olando Kepurė shore cliff and contributing an average of 50% of the sediment. This mathematically fairly simple site-to-site quantification approach applied here on the environmentally important fine-fraction could also be used with any other parameters characterizing identified sources. Our study is focused upon the stable, mineralogical components of the “sediment archive”, which offer a time-integrated, net-effect reflection of the combined processes of an entire environmental system, and recorded for each individual site of accumulation.
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| 19. |
- Ketzer, João Marcelo, et al.
(author)
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Near seafloor methane flux in the world's largest human-induced dead zone is regulated by sediment accumulation rate
- 2024
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In: Marine Geology. - : Elsevier. - 0025-3227 .- 1872-6151. ; 468
-
Journal article (peer-reviewed)abstract
- The vast oxygen-depleted area of the central Baltic Sea is the largest human-induced dead zone in the world with 70,000 km(2) or approximately three times the second largest one in the Gulf of Mexico. Methane occurs in high concentrations in bottom waters (3200 nM) and sediments (30 mM), and its dynamics is better constrained for the water column, but still poorly understood on sediments. Here we show that sediment accumulation rate plays a major role in regulating the quantity of organic matter and its residence time in the sulphate reduction and methanogenesis zones and, therefore, affects methane generation, consumption, and diffusive flux in sediments near the seafloor (< 1 m). High fluxes found in high sediment accumulation rate areas and competition for substrate (organoclastic sulphate reduction vs. anaerobic oxidation of methane with sulphate), compromise the ability of the thin microbial filter to consume and prevent methane diffusion through the seafloor.
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| 20. |
- Larson, Magnus, et al.
(author)
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Swash-zone sediment transport and foreshore evolution: field experiments and mathematical modeling
- 2004
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In: Marine Geology. - : Elsevier BV. - 0025-3227. ; 212:1-4, s. 61-79
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Journal article (peer-reviewed)abstract
- Data from field experiments carried out in the swash zone on two Pacific beaches in Japan were analyzed to determine net sediment transport rates and the resulting foreshore response. The experiments involved artificial modification of the foreshore slope with a bulldozer, either making the slope steeper or milder, after which a wide range of measurements were performed as the slope evolved back towards its equilibrium value under the action of the incident waves. A sediment transport formula was developed to predict the net transport rate over many swash cycles and compared with the derived transport rates from the surveys of the foreshore. This formula was then combined with the conservation equation for sediment volume to yield a mathematical model for simulating the foreshore evolution under varying waves and water level. Predictions by the model were compared to measurements yielding satisfactory agreement, although the optimum values on the main calibration coefficient displayed some variation between experiments. Further analysis of a limited number of cases indicated that this coefficient may be dependent upon the ratio between the incident wave period and the swash period, which characterizes the interaction between individual waves in the swash zone. A simple analytical solution was also derived for a schematized foreshore shape to estimate the typical time scale of the morphological response. (C) 2004 Elsevier B.V. All rights reserved.
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| 21. |
- Larsson, Olof, 1962, et al.
(author)
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The transition from glacimarine to marine conditions during the last deglacieation in the eastern Skagerrak
- 2007
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In: Marine Geology. - 0025-3227. ; 241, s. 45-61
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Journal article (peer-reviewed)abstract
- The paleoceanographic and paleoenvironmental evolution is described in the eastern Skagerrak. Separable stratigraphic units in seismic profiles and twelve piston cores document a changing balance between erosion and accumulation since the latest deglaciation. sediment supply and water depth but also whether the water mass is stratified or not are the important parameters in the processes controlling the depositional environment. The cores can be divided into two main units: a lower, well consolidated and clay-rich glacimarine mud with low organic content, and a silty, sandy, marine mud with relatively high organic content. The boundary between these two main units consists of an erosional surface, overlain by a coarse-grained lag. The deposition of the lower glacimarine mud started directly after deglaciation, at about 18.0 kyr BP. A major change in the sedimentation conditions at about 9.0 kyr BP led to a change from depositional to erosional conditions. The erosion has presumably removed a great part of the earlier deposits, creating the erosional surface which is present in the entire study area. Several dated samples above and below the erosional surface indicate a hiatus of about 10 kyr. In the south, the conditions changed again at about 5.0 cal kyr BP, allowing accumulation of the marine mud, while in the northern part erosive conditions continue to prevail. In the northern part, the marine mud is only deposited in limited areas, preferably sheltered areas along the coast.
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| 22. |
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| 23. |
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| 24. |
- Rebesco, Michele, et al.
(author)
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Contourites and associated sediments controlled by deep-water circulation processes: State of the art and future considerations
- 2014
-
In: Marine Geology. - : Elsevier BV. - 0025-3227. ; 352, s. 111-154
-
Journal article (peer-reviewed)abstract
- The contourite paradigm was conceived a few decades ago, yet there remains a need to establish a sound connection between contourite deposits, basin evolution and oceanographic processes. Significant recent advances have been enabled by various factors, including the establishment of two IGCP projects and the realisation of several IODP expeditions. Contourites were first described in the Northern and Southern Atlantic Ocean, and since then, have been discovered in every major ocean basin and even in lakes. The 120 major contourite areas presently known are associated to myriad oceanographic processes in surface, intermediate and deep-water masses. The increasing recognition of these deposits is influencing palaeoclimatology & palaeoceanography, slope-stability/geological hazard assessment, and hydrocarbon exploration. Nevertheless, there is a pressing need for a better understanding of the sedimentological and oceanographic processes governing contourites, which involve dense bottom currents, tides, eddies, deep-sea storms, internal waves and tsunamis. Furthermore, in light of the latest knowledge on oceanographic processes and other governing factors (e.g. sediment supply and sea-level), existing facies models must now be revised. Persistent oceanographic processes significantly affect the seafloor, resulting in large-scale depositional and erosional features. Various classifications have been proposed to subdivide a continuous spectrum of partly overlapping features. Although much progress has been made in the large-scale, geophysically based recognition of these deposits, there remains a lack of unambiguous and commonly accepted diagnostic criteria for deciphering the small-scaled contourite facies and for distinguishing them from turbidite ones. Similarly, the study of sandy deposits generated or affected by bottom currents, which is still in its infancy, offers great research potential: these deposits might prove invaluable as future reservoir targets. Expectations for the forthcoming analysis of data from the IODP Expedition 339 are high, as this work promises to tackle much of the aforementioned lack of knowledge. In the near future, geologists, oceanographers and benthic biologists will have to work in concert to achieve synergy in contourite research to demonstrate the importance of bottom currents in continental margin sedimentation and evolution.
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| 25. |
- Reghellin, Daniele, et al.
(author)
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The relationship between wet bulk density and carbonate content in sediments from the Eastern Equatorial Pacific
- 2013
-
In: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 344, s. 41-52
-
Journal article (peer-reviewed)abstract
- Sediment cores collected from the Eastern Equatorial Pacific Ocean display a clear positive second-order relationship between wet bulk density (WED) and carbonate content. This has long interested the paleoceanography community because detailed Gamma Ray Attenuation Porosity Evaluator (GRAPE) measurements, which approximate WBD, might be used to determine records of carbonate content at very high temporal resolution. Although general causes for the relationship are known, they have not been presented and discussed systematically on the basis of first principles. In this study, we measure the mass and carbonate content of 50 sediment samples with known WBD from Site U1338, before and after rinsing with de-ionized water; we also determine the mass related proportion of coarse (>63 mu m) material. Samples exhibit clear relationships between WBD, carbonate content, mass loss upon rinsing, and grain size. We develop a series of mathematical expressions to describe these relationships, and solve them numerically. As noted by previous workers, the second-order relationship between WBD and carbonate content results from the mixing of biogenic carbonate and biogenic silica, which have different grain densities and different porosities. However, at high carbonate content, a wide range in WBD occurs because samples with greater amounts of coarse carbonate have higher porosity. Moreover compaction impacts carbonate particles more than biogenic silica particles. As such, a single two-component equation cannot be used to determine carbonate content accurately across depth intervals where both the porosity and type of carbonate vary. Instead, the WBD-carbonate relationship is described by an infinite series of curves, each which represents mixing of multiple sediment components with different densities and porosities. Dissolved ions also precipitate from pore space during sample drying, which adds mass to the sediment. Without rinsing samples, simple empirical relationships between WBD and carbonate content are further skewed by salt dilution.
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| 26. |
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| 27. |
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| 28. |
- Sanchez, Guillaume, et al.
(author)
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Post-spreading deformation and associated magmatism along the Iberia-Morocco Atlantic margins : Insight from submarine volcanoes of the Tore-Madeira Rise
- 2019
-
In: Marine Geology. - 0025-3227 .- 1872-6151. ; 407, s. 76-93
-
Journal article (peer-reviewed)abstract
- A new high-resolution bathymetric map combined with a regional Digital Elevation Model (DEM) analysis reveal the modalities of occurrence and emplacement of post-spreading magmatism along the NNE-SSW oriented, 1000 km long Tore-Madeira Rise (TMR) as well as its relationship with the activity of major fault systems including the Estremadura Fault System (ESF) and the Azores-Gibraltar Fracture Zone (AGFZ). Morphological and structural analysis of the bathymetric map were performed to map volcanic features such as eruptive cones, vents and fissures together with faults along the TMR. The new bathymetric map shows that the main NNW-SSE seamount alignment is formed by three structurally distinct volcanic massifs, the Tore, the Josephine and the Southern Volcanic Groups. The majority of the volcanoes of each group emplaced within or along specific portion of pre-existing faults (ESF and AGFZ) including splay fault, releasing bend, fault tips and interaction zones between different segments. Magmas were channelled into sub-vertical pre-existing lithospheric faults that acted as preferential pathways for the vertical magma ascent. Migration and final eruption of magma are controlled by the local stress variation induced by complex fault geometries, change in plate kinematics as well as strong shear zone anisotropy as suggested by the emplacement within localised areas of transtension. We conclude that post-spreading magma emplacement in the southern part of the Iberia margin was related to the development of a transtensional plate boundary between the Iberian and African Plate during the Late Cretaceous. More generally, our findings emphasize that the distribution of volcanism as the expression of the interaction between shallow plate tectonic and mantle processes should be included in plate kinematic reconstruction. This study also demonstrates that the accurate mapping of oceanic seafloor is pivotal to better understand tectono-magmatic evolution of volcanic seamount chains and geological processes in oceanic domains.
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| 29. |
- Seaman, Paul, et al.
(author)
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New multibeam mapping of the unique Ikaite columns in Ikka Fjord, SW Greenland
- 2022
-
In: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 444
-
Journal article (peer-reviewed)abstract
- Ikka Fjord in SW Greenland is world famous for its submarine, cold-water craving ikaite (CaCO3·6H2O) tufa columns. Due to the uniqueness of the columns, Ikka Fjord is declared a protected area by the Greenlandic authorities. In the summers of 2018–19, multibeam sonar bathymetry and aerial drone photogrammetric surveys were made in Ikka Fjord mapping and counting the columns and comparing the results to data from geophysical surveys of the fjord in 1995–96. The new surveys provide highly detailed maps of the fjord bathymetry and its columns, their height and position, and several hitherto unknown pockmarks in the seabed. A total of 938 individual columns and structures ranging 0.5–20 m in height from the sea floor were identified: a number surpassing the 678 taller columns (> 1 m) known from previous mapping. Our results support previous observations that the columns are restricted to the spatial extents of the Grønnedal-Íka igneous complex. The new survey data show that column distribution exhibits lineations and variable density over the fjord floor, notably that the innermost central deep part is free of columns. The tallest columns are observed to grow up to the halocline at approximately 2–4 m water depth. The majority of columns have reached only 15–50% of their growth potential. The ~60 columns of maximum growth stand in clusters, interpreted as representing exceptionally favourable growth settings. New seawater data collected in 2019 shows a worrying increase in temperature since the previous measurements in 1995 and 2007–2009, which could potentially affect the stability of the delicate columns of Ikka Fjord.
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| 30. |
- Sohlenius, Gustav, et al.
(author)
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Development of anoxia during the Holocene fresh-brackish water transition in the Baltic Sea
- 2001
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In: MARINE GEOLOGY. - : ELSEVIER SCIENCE BV. - 0025-3227. ; 177:3-4, s. 221-242
-
Journal article (peer-reviewed)abstract
- One of the most pronounced environmental changes during the Holocene Baltic Sea history was the transition from the freshwater Ancylus Lake to the brackish water Litorina Sea. The establishment of brackish conditions during this transition (the A/L) was c
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| 31. |
- Suteerasak, Thongchai, et al.
(author)
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Deposition rates and C-14 apparent ages of Holocene sediments in the Bothnian Bay of the Gulf of Bothnia using paleomagnetic dating as a reference
- 2017
-
In: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 383, s. 1-13
-
Journal article (peer-reviewed)abstract
- Three 6-m-long cores of sediments were collected in the northern, middle and southern part of the Bothnian Bay. The sediments were dated by paleomagnetic dating techniques, constrained by magnetic properties and geochemical data. The results indicate the ages of the sediments in the bottom part of the cores in the northern, middle and southern parts of the Bothnian Bay to be approximately 5300 years BP, 5350 years BP and 3500 years BP, respectively. The deposition rate calculated from the estimated ages at various depths show that the deposition rate was generally in the range 0.5-1.5 mm/year but it was higher in the southern part than in the middle and northern parts of the bay. There was a significant increase in the deposition rate at ca 2200 years BP, recorded in all three cores, a rate varying between 2.47 and 3.07 mm/year and lasting until ca 1840 years BP. A proposed constant uplift rate of the crust during the period ca 5500 years BP to present is thus not reflected by a constant deposition rate. The peaks in deposition rates at ca 2200-1840 years BP were followed by a decrease in salinity. This phenomenon is suggested to be caused by crustal uplift, with a threshold being formed in the southern part of the bay, thereby increasing the reactivation of bottom sediments and reducing the inflow of brackish water from the Bothnian Sea. The C-14 ages of the sediments reveal differences in age compared with the paleomagnetic ages. In the southern core, the C-14 ages are ca 1350 years older, and in the north, the age offset is mixed. The reactivation and re-deposition of sediments is argued to be the reason for the apparent C-14 age differences. This finding demonstrates that C-14 cannot be used for the dating of Bothnian Bay sediments unless the radiocarbon age offset has been determined.
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| 32. |
- Tesi, Tommaso, et al.
(author)
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Source, diagenesis, and fluxes of particulate organic carbon along the western Adriatic Sea (Mediterranean Sea)
- 2013
-
In: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 337, s. 156-170
-
Journal article (peer-reviewed)abstract
- In this study, we investigated the modern organic carbon (OC) cycling along the clinoform-shaped deposit that developed after the attainment of the modern sea-level in the Adriatic Sea (similar to 5.5 kyr cal BP). Newly acquired data were combined with published results to characterize the (i) origin, (ii) diagenesis, and (iii) fluxes of OC along the Adriatic clinoform. delta C-13, Delta C-14, and lignin phenols were used to constrain the composition of CC accumulating in surface sediments. Sediment cores collected at different water depths were used to describe the early diagenesis during burial in different regions. In addition, on the basis of an extensive number of accumulation rates and CC data, we assessed the flux of CC to the seabed and its burial. Our results showed that terrigenous CC is the dominant CC source in the Po prodelta mainly in the form of pre-aged soil-derived CC and vascular plant fragments. Along the clinoform, both Delta 14C and the concentration of lignin-derived phenols decreased with increasing distance from the Po prodelta indicating the influence of an additional pool of aged CC that gradually becomes more important because of its selective preservation during the sediment transport. As a result, degradation rates (k) decreased along the clinoform as a function of the sediment oxidative history. The calculated half-life of reactive OC (t(1/2)) was similar to 14.6 yrs in the Po prodelta whereas topset/forest deposits south of this region exhibited higher values, similar to 100 yrs, indicating the presence of refractory material. In the distal bottomset region, the tip was particularly high ranging from similar to 255 to similar to 912 yrs. Because of the significant southward component of the sediment transport, the CC deposition in the southern surface sediments exceeded the local CC input via rivers (ratio deposition/input 12). Conversely, the northern Adriatic was characterized by a marked imbalance (ratio deposition/input 0.3-0.5). According to our calculations, the CC flux to the seabed along the clinoform was similar to 309 Gg of C per year whereas the OC burial was similar to 180 Gg of C per year, corresponding to an overall burial efficiency of similar to 59%.
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| 33. |
- Thurber, Andrew R., et al.
(author)
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Stable isotope signatures and methane use by New Zealand cold seep benthos
- 2010
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In: MARINE GEOLOGY. - 0025-3227. ; 272:1-4, s. 260-269
-
Journal article (peer-reviewed)abstract
- The carbon isotopic composition of seep faunal tissue represents a time-integrated view of the interaction between biology and the biogeochemical gradients within the environment. Here we provide an initial description of carbon and nitrogen stable isotope signatures of dominant symbiont-bearing megafauna and heterotrophic mega- and macrofauna from 10 methane-seep sites on the continental margin of the North Island of New Zealand (662–1201 m water depth). Isotopic signatures suggest that sulfide oxidation supports symbiont-bearing taxa including solemyid and vesicomyid bivalves, and methanotrophic symbionts are present in the seep mussel Bathymodiolus sp. Multiple species of Frenulata (Siboglinidae) are present and have a range of isotopic values that are indicative of both thiotroph- and methanotroph-based nutrition. Isotopic composition of the tubeworm Lamellibrachia sp. varied by 23.3‰ among individuals although there was no consistent difference among sites. Variation in methane use by heterotrophic fauna appears to reflect the availability of hard vs. soft substrate; macrofauna on hard substrates had high δ13C signatures, reflecting consumption of photosynthetic-derived organic matter. Two unique, biotic assemblages were discovered to be fueled largely by methane: a hard-substrate, multi-phyla sponge-associated community (inhabiting the sponge Pseudosuberites sp.) and a soft-sediment assemblage dominated by ampharetid polychaetes. Isotope signatures yield estimates of 38–100% and 6–100% methane-derived carbon in sponge associates and ampharetid-bed macrofauna, respectively. These estimates are comparable to those made for deeper methane seeps at the Florida Escarpment (3290 m) and Kodiak, Alaska seeps (4445 m). The overall high use of methane as a carbon source by both symbiont-bearing and heterotrophic fauna suggests that New Zealand methane seeps are an ideal model system to study the interaction among metazoans, bacteria, archaea, and their resulting effect on methane cycles.
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| 34. |
- Tuuling, Igor, et al.
(author)
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Seismic stratigraphy, architecture and outcrop pattern of the Wenlock-Pridoli sequence offshore Saaremaa, Baltic Sea
- 2011
-
In: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 281:1-4, s. 14-26
-
Journal article (peer-reviewed)abstract
- The Wenlock-Pridoli sequence has been subdivided and mapped offshore Saaremaa in the Baltic Sea by means of high resolution seismic reflection profiling. The most striking and consistent seismic reflectors correlate with contrasting lithological boundaries of the Silurian regional stages, the Jaani/Jaagarahu (S(8)), the Jaagarahu/Rootsikula (S(10)), the Rootsikula/Paadla (S(11)). the Paadla/Kuressaare (S(12)), the Kuressaare/Kaugatuma (S(13)) and the Kaugatuma/Ohesaare (S(14)) stages, which often coincide with erosional disconformities on Saaremaa. The shallow-shelf Silurian sequence that crops out on Saaremaa is also exposed in the closest offshore area of the island. Due to the westerly to south-westerly increasing erosional cut below the Baltic, the deeper facies varieties that are concealed in southern Saaremaa, are revealed and exposed at the seafloor towards Gotland. This is particularly well expressed in the Jaagarahu Stage, which undergoes a fades change with significant increase in thickness on the basinal slope of the Baltic Silurian Basin, both onshore and offshore Saaremaa. The Silurian sequence overlying the Jaagarahu Stage does not show any considerable thickness or fades changes neither below nor offshore Saaremaa. Offshore Saaremaa, seismic reflectors limiting new deeper facies subunits in the Jaagarahu Stage become either successively or simultaneously exposed inside the Vilsandi (S(8)-S(9)) respectively the Maasi-Tagavere (S(9)-S(10)) seismic units towards Gotland. These outcrop patterns were largely formed by two different erosional agents that during different time periods have played a considerable role in the formation of the present day Baltic Sea depression. Hence, the gradually south-westerly deepening cuesta landscape formed by the Cenozoic erosion, namely the Silurian Klint and the plateaus north and south of it, discloses progressively deeper part of the Baltic Silurian Basin. The deeper facies subunits are exposed rapidly by the submeridional erosional incisions of the Pleistocene glaciers. Except for the erosional component, there appears also a distinct tectonic factor in the genesis of the present Baltic Sea depression. Today, the coeval Silurian rocks that once were formed in separate facies belts, i.e. in different depth intervals of the same sedimentary basin on Saaremaa and on Gotland, are presently located at about equal altitude.
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| 35. |
- Tuuling, Igor, et al.
(author)
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The Llandovery-lowermost Wenlock sequence in the Baltic Sea between Saaremaa and Gotland : subdivision, thicknesses and correlation, based on marine seismic studies
- 2009
-
In: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 267:02-jan, s. 55-70
-
Journal article (peer-reviewed)abstract
- The Llandovery-lowermost Wenlock sequence in the Baltic Sea between Saaremaa and Gotland has been studied by means of high resolution seismic reflection profiling. The number and the positions of the seismic reflectors within this sequence change considerably even within short distances, thus showing a high lateral inconsistency both in lithology and thickness. Stratigraphically two unambiguous (S-1 and S-2) and two roughly fixed trans-Baltic seismic reflectors (S-5 and S-7) enabled us to distinguish the pre-Adavere, the Adavere (S-1-S-2 and S-2-S-5) and the Mustjala seismic units (S-5-S-7) and to follow their east-westerly changes across the Baltic. The seismic signatures and thicknesses of these units undergo a sharp transformation midway Baltic, dividing between the Saaremaa type and the Gotland type of Llandovery-lowermost Wenlock sections. This is due to a short and steep northeast-southwest facies transect that was induced by a well differentiated bathymetry in the intracratonic Palaeobaltic basin, thus clearly distinguishing the shallow-shelf (basinal), the slope (transitional) and the deep-shelf (basinal) areas. The slope is furthermore accentuated by the intensive submarine erosion and channelling during the Late Ordovician and Early Silurian times. Thus, the Saaremaa type of section includes the inner to outer shallow-shelf transect, where the pre-Adavere and Adavere units are decreasing in thickness, and the Mustjala unit is increasing in thickness towards Gotland. In the slope area offshore Gotland, all the Llandovery-lowermost Wenlock units thin out rapidly towards the deep-shelf area in south to southeast and the thickness of the pre-Adavere and Adavere units approach zero. Similar features of submarine erosion on Gotland and around the Estonian Latvian border reveal that an unstable basinal slope, from the point of sediment accumulation, extended over large areas along the shallow-shelf edge of the Palaeobaltic basin during the latest Ordovician and earliest Silurian times. Seismic data suggest that the uppermost unidentified subsurface of the Silurian succession in northern Gotland includes a considerable amount of marlstone layers that are coeval with the Mustjala Member in Estonia.
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| 36. |
- van Helmond, Niels A G M, et al.
(author)
-
Seasonal hypoxia was a natural feature of the coastal zone in the Little Belt, Denmark, during the past 8 ka
- 2017
-
In: Marine Geology. - : Elsevier. - 0025-3227 .- 1872-6151. ; 387, s. 45-57
-
Journal article (peer-reviewed)abstract
- The extent of the hypoxic area in the Baltic Sea has rapidly expanded over the past century. Two previous phases of widespread hypoxia, coinciding with the Holocene Thermal Maximum (HTM; 8–4 ka before present; BP) and the Medieval Climate Anomaly (MCA; 2–0.8 ka BP), have been identified. Relatively little is known about bottom water redox conditions in the coastal zone of the Baltic Sea during the Holocene, however. Here we studied the geochemical composition of a sediment sequence from a currently seasonally hypoxic site in the Danish coastal zone, the Little Belt, retrieved during Integrated Ocean Drilling Program Expedition 347 (Site M0059). The base of the studied sediment sequence consists of clays low in organic carbon (Corg), molybdenum (Mo) and iron sulfides (Fe-sulfides), and rich in iron oxides (Fe-oxides), indicative of a well-oxygenated, oligotrophic (glacial) meltwater lake. An erosional unconformity separates the glacial lake sediments from sediments that are rich in Corg. The absence of Mo, in combination with high Corg/S values, indicates that these sediments were deposited in a highly productive, well-oxygenated freshwater lake. The transition to modern brackish/marine conditions was very rapid, and subsequent continuous sequestration of Mo in the sediment and high ratios of reactive iron (FeHR) over total Fe (FeTOT) suggest (seasonal) hypoxia occurred over the last ~ 8 ka. Maxima in sediment Corg, Mo and FeHR/FeTOT ratios during the HTM and MCA suggest that the hypoxia intensified. Our results demonstrate that the Little Belt is naturally susceptible to the development of seasonal hypoxia. While periods of climatic warming led to increased deoxygenation of bottom waters, high nutrient availability in combination with density stratification were likely the main drivers of hypoxia in this part of the coastal zone of the Baltic Sea during the Holocene.
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| 37. |
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| 38. |
- Witkowski, Jakub, et al.
(author)
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Rethinking the chronology of early Paleogene sediments in the western North Atlantic using diatom biostratigraphy
- 2020
-
In: Marine Geology. - : Elsevier BV. - 0025-3227. ; 424
-
Journal article (peer-reviewed)abstract
- Ocean Drilling Program (ODP) Site 1051 (Blake Nose, western North Atlantic) is of crucial importance for reconstructing diatom evolution and biosiliceous sedimentation patterns through the early Cenozoic period of extreme greenhouse warmth followed by the progressive global cooling. The magnetostratigraphy in Hole 1051A, however, has been subject to divergent interpretations resulting in multi-million-year age control uncertainties, especially for events surrounding the early to middle Eocene transition. To resolve these uncertainties, we compare the stratigraphy of Hole 1051A to the neighboring Holes 1050A, C. We compile the published biomagnetostratigraphic data for both sites and identify three possible magnetostratigraphic solutions for Hole 1051A, the difference being the number of hiati and their duration. In order to identify the most plausible magnetostratigraphic solution for Hole 1051A, we employ the graphic correlation method, in which we compare the depth of individual magnetic reversals in both study sites against an independent proxy, i.e., 49 diatom evolutionary events identified in Holes 1050A,C and 1051A. The distribution of diatom bioevents lends strong support to the presence of two major hiati in both study sites: the upper hiatus juxtaposes magnetozone C21n on C22n, and the lower hiatus juxtaposes magnetozone C23n on C24n, eliminating the record of the initial part of the Early Eocene Climatic Optimum. Diatom, calcareous nannofossil and foraminiferal biostratigraphic markers also indicate that Hole 1051A terminated within magnetozone C28n rather than C27n. This age interpretation is strongly supported by the alignment of high-resolution weight percent biogenic SiO2 records from both study sites. The revised age models developed here for Holes 1050A,C and 1051A have profound consequences for interpretations of western North Atlantic paleoceanographic and paleoclimatic history through the early Paleogene. We propose a revised labelling of the early Eocene carbon cycle perturbations identified to date in Hole 1051A, and show how published Blake Nose δ30Si records change when data from Sites 1050 and 1051 are rescaled to the age models proposed herein. We emphasize that these refinements to the stratigraphy of Sites 1050 and 1051 are based on a study of diatom bioevents, which are here identified and calibrated to the Geomagnetic Polarity Timescale. This successful application of diatom biostratigraphy is a substantial advance toward their future utility in providing high-resolution age control for Paleogene deep-sea sites.
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| 39. |
- Zhang, J., et al.
(author)
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Decadal-scale subaerial beach and dune evolution at Duck, North Carolina
- 2021
-
In: Marine Geology. - : Elsevier BV. - 0025-3227. ; 440
-
Journal article (peer-reviewed)abstract
- Thirty-nine years of high-resolution data from 1981 to 2019 surveyed by the Field Research Facility (FRF) of the US Army Corps of Engineers at Duck, North Carolina, in the United States, were analyzed for temporal and spatial characteristics of beach morphology evolution employing a range of statistical methods. In the study, emphasis was put on the response of the subaerial part of the beach profile to waves and water levels at several different spatial and temporal scales, ranging from weekly to decadal response. The profile data set was analyzed to determine the subaerial beach evolution, including both the influence of cross-shore sediment transport related to storms and the longshore transport affected by the FRF research pier. The analysis showed that adjacent profile lines exhibit similar beach morphology and evolution with high correlation regarding spatial and temporal patterns. The pier has a noticeable influence on the longshore sediment transport leading to erosion downdrift and accretion updrift of the pier; the dune in the FRF region is rather stable and resistant towards storm erosion, requiring combinations of runup height and water level (i.e., runup level) that reaches the dune face; and erosion high up on the subaerial part of the beach, including the dune, occurs on average due to storms with a return period of 5 years.
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